This invention relates to electronic switches and particularly to circuitry for symmetrically controlling the forward and reverse bias switching of semiconductor bridge switches. The invention further relates to circuitry for improving the turn-on response of semiconductor bridges by controlling the voltage reference and antisaturation of switched turn-off circuits for the bridges.
Electronic switches utilizing diode and transistor bridges are extensively used in communication and data systems to provide for high speed switching of information. For example, such switches are used in time division switching system applications for establishing recurrent, short duration connections for telephone call processing, conversation and supervision. Among the advantages of the switches are their low power consumption, fast acting time and small size compared to electromechanical switches.
Semiconductor bridges are customarily equipped with input and output signaling nodes and a pair of bias control nodes. Information signal transmission occurs between the input and output nodes and in response to the forward biasing of the bridge semiconductors by currents supplied to the bias control nodes. In the absence of the forward bias, the bridge semiconductors substantially block signal transmission between the input and output nodes.
A problem in prior art semiconductor bridge arrangements is that the quality of transmission is often impaired by circuit and operational imbalances in switching the bridge to and from its forward biased state. The impairment frequently arises due to mismatches in the forward bias currents used to drive the bridge, as well as, the sequential application and withdrawal of those currents to and from the bias control nodes of the bridge.
It is also a deficiency in prior art semiconductor bridges that the turn-on response time is often degraded by the circuits which control a switched turn-off and steady state reverse biasing of the bridge. The degradation generally affects the information handling capacity of the system employing the bridge and, importantly, tends to cause distortion in the formation signal switched through the bridge.
In view of the foregoing, it is apparent that a need exists for facilities to improve signal transmission quality through semiconductor bridges and particularly to reduce circuit and operational imbalances which contribute to signal distortion. A further need is to provide facilities for minimizing the deficiencies including impaired bridge turn-on response time and signal distortion.